Effective methods of recovery and/or separation of particular molecules such as gases, anions, amino acids, and others, from other molecules in water supplies, organic solvents, waste solutions, and industrial solutions and streams represent a real need in modern technology. These molecules are often present at low concentrations in solutions containing other molecules at much greater concentrations Likewise there is a need to concentrate these molecules so that an effective analysis using known methods can be carried out. Hence, there is a real need for a process to selectively recover and concentrate these molecules.
It is known that many cations present as solutes in a solvent such as water, existing either as the free cation or complexed by a ligand solute, are capable of additional complexation at binding sites initially held by H.sub.2 O or other weakly coordinated ligands or via ion pairing. These cations or cation-ligand complexes are characterized by their ability to selectivity form strong bonds with other strongly bonding ligand(s) solutes when the H.sub.2 O or other weakly coordinated ligands are released. See, for example, Smith et al., CRITICAL STABILITY CONSTANTS, 6 volumes, Plenum Press, New York, 1975, 1982, 1989., and Bard, et al., STANDARD POTENTIALS IN AQUEOUS SOLUTION, Marcel Dekker, New York, 1985. However, researchers have not previously been able to effectively incorporate these cation-ligand complexes, which are capable of further selective complexation, into separation systems where the behavior of the cation-ligand complex in the separation systems in comparison to that of the cation-ligand complex as a solute remains unchanged. Nor have researchers developed a system wherein the cation-ligand complex will remain in the separation system for use in repeated separations.
Many organic ligands have been attached to polymeric supports, such as polystyrene, but the properties of the support bound ligands are substantially different compared to the analogous unbound ligand as an aqueous solute. A review article on this subject is found in Volume 19 of the series "Critical Reports on Applied Chemistry", in Chapter 4 (pp.167-223) entitled CHELATING ION EXCHANGERS by A. Warshawsky, Edited by Streat et al., John Wiley and Sons, 1987. Attaching these organic ligands to hydrophobic supports substantially changes the properties of the ligand molecules.
Articles such as SILANE COMPOUNDS FOR SILYLATING SURFACES by E. P. Plueddemann, in "Silanes, Surfaces and Interfaces Symposium, Snowmass, 1985", Ed. by D. E. Leyden, Gordon and Breach Publishers, 1986, pp. 1-25 and SILANE COUPLING AGENTS by E. P. Plueddemann, Plenum Press, 1982, pp. 1-235 list many different types of organic materials which have been attached to silane compounds and discusses some of their properties. E. P. Plueddemann in METAL EXTRACTION FROM SOLUTION AND IMMOBILIZED CHELATING AGENTS USED FOR THIS PROCESS, Canadian Patent 1,196,618 issued Nov. 12, 1985 and others have reported in the patent literature other ligands which can be immobilized on silica gel and used to complex metal cations from aqueous solutions. However, the use of coordinating molecules covalently bound to solid materials to complex metal cations to the solid support and the subsequent use of additional coordination sites of the metal cation to perform specific separations with regard to gases, amino acids, anions, and other molecules has not been previously reported.
Researchers have had moderate success in using plain ion exchange beds to complex cations and then using the bound cations to effect separations. Articles such as DETERMINATION OF THE TWO-PHASE EQUILIBRIUM CONSTANTS OF COPPER Cu(II)-MODIFIED SILICA GELS USED IN LIQUID CHROMATOGRAPHY. by Guyon et al., Analytica Chimica Acta, 170 (1985) 311-317 describe such efforts with hydrophilic supports such as silica gel. Suzuki et al., in SEPARATION OF OLEFINIC COMPOUNDS, Japanese Kokai Patent number 75 05, 302 (Cl.16AO) published Jan. 21, 1985 report an example of the use of metals bonded to an ion exchange resin composed of hydrophobic supports such as polystyrene to effect separations. However, there has been no previous report of using bound coordination ligands covalently attached to a solid support, such as silica gel, and containing a complexed cation to effect separations. The use of the bound coordinating ligand rather than an ion exchange bed allows for both much greater stability and selectivity in maintaining the cation on the resin as well as a much greater variety of separations to be performed.
There is a particular need in modern society to (1) measure the concentrations of molecules in low parts per million (ppm) to low parts per billion (ppb) concentrations; (2) to remove low levels of toxic molecules from solutions such as potable and saline water; and (3) to recover valuable molecules which are present in solution at low concentrations. For example the allowable amount of ammonia in saline water in order for fish to live is approximately 1-2 parts per million. Present methods for analysis of these molecules at these levels are not accurate and/or are very time consuming. Furthermore, removal of the molecules is not selective, but is expensive and equipment intensive using present methods. Other present needs in industry which present utility opportunities for the use of solid supported ligand bound cations include removal of toxic anions such as CrO.sub.4.sup.2-, preparation of ultrapure salts (halide separations), preparation of ultrapure gases (O.sub.2 and other separations), separation of amino acids and amines and others. Thus, development of means to utilize the molecule complexing properties of complexes of cations with ligands attached to an inorganic support, such as silica gel or titanized silica gel, would be of the utmost importance for the repeated separation and concentration of certain molecules for analysis, and/or recovery purposes. The process of the present invention accomplishes this feat.